Interactive portable defibrillator

ABSTRACT

A portable, interactive medical electronic device exemplified by a defibrillator. The device obtains information about a patient&#39;s condition, such as ECG and transthoracic impedance data, directly from the patient, and information pertinent to the treatment of the patient indirectly through an operator of the device, and produces a medically appropriate action such as a defibrillation shock in response. Indirect information is obtained through information processing means that includes means for prompting the operator of the device and means for receiving the operator&#39;s responses thereto. Prompts may include both questions and instructions, and in one embodiment the information processing means obtains the assent of the operator before causing the defibrillation shock. Indirect information may include information as to whether the patient is conscious, and as to whether or not cardiopulmonary resuscitiation has been performed. The ECG and transthroacic impedance data may be collected through a common pair of electrodes. In one embodiment the device produces an indication that the ECG data is invalid if the transthoracic impedance data indicates excessive motion on the part of the patient. When a difibrillation shock is determined to be medically appropriate, a control signal is produced that causes the charging of an energy storage means and the subsequent discharging of such energy storage means through the patient without further operator intervention. The device also includes a tape recorder for allowing later analysis of the use of the device, and means for holding the tape recorder drive means in a disengaged position until the device is opened for use. The device also includes testing means for enabling a person to test the condition of the device without opening the case in which it is enclosed, means for producing and recording a distinctive sound when and if a defibrillation pulse is delivered, and means for allowing the electrodes to be quickly disconnected so that emergency personnel can conveniently use the electrodes with their own equipment.

BACKGROUND OF THE INVENTION

It is well known that the probability of surviving a heart attack oftendepends critically on the speed with which appropriate medical care isprovided. One of the most common and life threatening consequences of aheart attack is the development of a cardiac arrhythmia such asventricular fibrillation in which the heart is unable to pump asignificant volume of blood. When such an arrhythmia occurs, seriousbrain damage and death will invariably result unless a normal heartrhythm can be restored within a few minutes.

The most effective treatment for ventricular fibrillation is theapplication of a strong electric shock to the victim. By a mechanism notfully understood, such an electric shock frequently terminates thechaotic activity characteristic of arrhythmias, and restores the normalpumping action of the heart. Defibrillators for producing and deliveringsuch shocks have been known and successfully used for many years.However, the size and cost of prior defibrillators, coupled with therisk they pose if used improperly, have restricted the use ofdefibrillators to hospitals and to emergency medical facilities. Manylives would be saved each year if defibrillators could be made moreimmediately available to heart attack victims.

A large number of heart attacks occur to people who have a history ofcardiac problems, and who are therefore known to be at risk. In recentyears, many family members of high risk patients have received trainingin cardiopulmonary resuscitation, a technique designed to maintain someblood flow even if the heart is in fibrillation or has stopped beatingaltogether. Such training is helpful because a large percentage ofrepeat heart attacks occur in the presence of a family member.Unfortunately, it has to date not been possible to provide the familymembers of high risk patients with access to the generally moreeffective technique of defibrillation, because of the difficulty ofdesigning a defibrillator that is portable and that can be safely andeffectively used by nonmedical personnel.

SUMMARY OF THE INVENTION

The present invention provides a personal defibrillator that isportable, easy to use, and comparatively inexpensive. The defibrillatoris sufficiently compact and lightweight to be kept at all times in theimmediate vicinity of a person known to be at risk to heart attacks. Inaddition, the defibrillator is designed to be used interactively, sothat a properly trained, nonmedical operator can safely and effectivelyoperate the device.

In one embodiment, the present invention comprises an interactive,medical electronic device that is capable of obtaining information abouta patient's condition, such as ECG data, directly from the patient, andinformation pertinent to the treatment of the patient indirectly throughan operator of the device, and for producing a medically appropriateaction such as a defibrillation shock in response. Sensor means are usedto obtain direct information concerning the condition of the patient,and indirect information is obtained through information processingmeans that includes means for prompting the operator of the device, andmeans for receiving the operator's responses thereto. The device alsoincludes control means for producing a control signal when the directand indirect information indicates that the medically appropriate actionshould be taken, and output means responsive to the control signal forproducing such action. The information processing means may also includemeans for communicating questions and instructions to the operator, andmeans for obtaining the assent of the operator before producing thecontrol signal. In one preferred embodiment, the questions communicatedto the operator are designed such that appropriate responses are eitherYES or NO. The indirect information obtained from the operatorpreferably includes information as to whether the patient is conscious,and as to whether or not cardiopulmonary resuscitation has beenperformed.

In a further embodiment, the present invention comprises a defibrillatorhaving means for simultaneously obtaining electrocardiogram andtransthoracic impedance data from a patient, and means for producing anindication that the electrocardiogram data is invalid if thetransthoracic impedance data indicates excessive motion on the part ofthe patient. In a preferred embodiment, the defibrillator includes meansfor producing analog electrocardiogram and motion signals, the motionsignal being based on transthoracic impedance, and means for alternatelysampling the electrocardiogram and motion signals and providingcorresponding digital samples. A processor stores the electrocardiogramsamples obtained during a time interval, and examines the motion samplesprovided during that time interval for indications of excessive motionon the part of the patient. If excessive motion is detected, the timeinterval is restarted. In a further preferred embodiment,electrocardiogram and transthoracic impedance data is collected througha common pair of electrodes.

In another embodiment of the present invention, a defibrillator isprovided that includes information processing means for determiningwhether a defibrillation shock should be delivered and for providing afirst control signal if the defibrillation shock should be delivered,and defibrillation means responsive to the first control signal forproducing the shock. The defibrillation means includes energy storagemeans and means responsive to the first control signal for charging theenergy storage means up to a threshold level and then discharging itthrough the patient. Timing means is provided for discharging the energystorage means through the patient if the charge on the energy storagemeans does not reach the threshold level within a predetermined timeafter the first control signal is provided. In a preferred embodiment,the defibrillation means provides a second control signal whenever thestorage means is discharged, and the information processing meansincludes means for suspending its operations from the time that thefirst control signal is provided until the second signal is providedonly upon command from an operator of the defibrillator, and thedefibrillation means then proceeds to automatically charge and dischargethe energy storage means.

In another embodiment, the present invention includes means for allowingmedical personnel to analyze the circumstances in which the device wasused. Such means comprises a tape recorder for recording signalsrepresenting medical information on magnetic tape, a source ofelectrical power, and switch means for connecting the source ofelectrical power to the tape recorder when the tape recorder is to beoperated. The tape recorder includes drive means for driving the tapepast a recording means, a portion of the drive means being movablebetween a first position in which the drive means engages and drives thetape, and a second position in which the tape is at least partiallydisengaged from the drive means. The movable portion of the drive meansis biased towards the first position, and the tape recorder includes aconductive fusible link positioned to hold such portion in the secondposition. The fusible link is connected to pass an electrical currentwhen the switch means connects the source of electrical power to thetape recorder, the fusible link being adapted to fuse when an electricalcurrent is passed through it. The tape recorder is used to permanentlyrecord information concerning the use of the device. The fusible linkprevents damage to the tape during long periods of storage before thedevice is used.

In another embodiment, the device of the present invention comprises acase, a battery enclosed within the case, and testing means enclosedwithin a case for enabling a person to test the condition of the devicewithout opening the case. The testing means includes means for testingthe device when battery power is applied and for producing an audibletone indicating the test results, and a magnetically operated switchadapted to connect the battery to the means for testing the condition ofthe device when a magnet is placed in the vicinity of the switch. Thedevice of the present invention, including the battery, may therefore beplaced within a completely sealed case, while still providing a meanswhereby the device or battery may be tested without opening the case orbreaking the seal.

In another embodiment of the present invention, a defibrillator isprovided having means for detecting that a defibrillation pulse has beendelivered to the patient. The defibrillator includes a conductor throughwhich the pulse is delivered, means responsive to the presence ofcurrent in the conductor for producing a magnetic field, means forproducing a sound in response to the production of the magnetic field,and means for detecting the sound. The defibrillator may also includemeans for recording such sound on magnetic tape.

In another embodiment of the present invention, a defibrillator isprovided having electrodes for attachment to a patient, defibrillationmeans for providing a pulse of electrical energy, and connector meansfor connecting the defibrillation means to the electrodes. The connectormeans includes plug means adapted to permit the electrodes to be quicklydisconnected from the defibrillation means. When emergency medicalpersonnel arrive on the scene, this feature enables them to avoid delayby plugging the electrodes of the present invention directly into theirown equipment.

These and other features and advantages of the invention will becomeapparent in the detailed description and claims to follow, taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a sealed defibrillator according to thepresent invention.

FIG. 2 is a perspective view of the defibrillator of FIG. 1 with thecover plate removed and the electrodes withdrawn.

FIG. 3a-3h is a series of eight views of the display of thedefibrillator during different stages of defibrillator operation.

FIG. 4a-b is a block diagram of the electronic components of thedefibrillator.

FIG. 5 is a circuit diagram of the processor controller.

FIG. 6 is a cross-sectional view of the wave shaping inductor andassociated sound producing means of the defibrillator.

FIG. 7a-f is a flow chart of a program for operation of the dataprocessor of the defibrillator.

DETAILED DESCRIPTION OF THE INVENTION

Referring initially to FIGS. 1 and 2, one preferred embodiment of thepresent invention is shown as comprising defibrillator 10 having body12, cover plate 14, and carrying handle 16. To use the defibrillator, anoperator breaks seal 18 and removes cover plate 14. The cover plateincludes a pin 20 which is positioned in opening 22 of body 12 beforethe cover plate is removed. Removal of the cover plate withdraws pin 20and activates the defibrillator, as described below. The underside ofcover plate 14 includes printed instructions 24 for facilitating correctusage of the device.

Prior to removal of the cover plate, a pair of electrodes 30, 36 andassociated cable 42 are held in the space between cover plate 14 andbody 12. When the cover plate is removed, the electrodes and cable maybe withdrawn for use, as indicated in FIG. 2. Electrodes 30 and 36include adhesively surfaced outer portions 32 and 38 respectively, andrespective inner portions 34 and 40 that are coated with a conductivegel for making electrical contact with a patient's body. Cable 42includes separate cables 44 and 46 connected to electrodes 30 and 36,respectively. Cable 42 includes plug 48 which permits the electrodes tobe quickly disconnected from the defibrillator, so that emergencymedical personnel arriving on the scene can avoid delay by pluggingelectrodes 30 and 36 directly into their own equipment. Electrode 36includes diagram 37 illustrating the correct placement of the electrodeson the patient.

The body 12 of the defibrillator includes an LCD display 50, andpushbutton switches 52, 54 and 56. Display 50 is used for prompting theoperator of the defibrillator, as described in greater detail below.Switches 52 and 54 are labeled with the words YES and NO, respectively,and are used by the operator to respond to questions presented viadisplay 50. Switch 56 is labeled "SHOCK," and is used by the operator atthe appropriate time to initiate application of a defibrillation shock.

A pair of scissors 60 may also be carried in the space between body 12and cover plate 14. The scissors are used to remove the patient'sclothing, to facilitate placement of electrodes 30 and 36.

Prior to use, the defibrillator of the present invention is completelycontained within the portable, compact unit illustrated in FIG. 1. Thisdesign makes it both practical and convenient to continuously keep thedefibrillator in the immediate vicinity of a patient known to be at riskwith respect to heart attacks. Seal 18, in combination with otherfeatures described below, helps assure the integrity of the unit duringprolonged periods of storage.

GENERAL OPERATION

The general operation of the defibrillator will now be described withreference to FIGS. 3a-h. When a heart attack occurs, the operatorremoves the cover plate, and the defibrillator is activatedelectronically. The operator is immediately directed to connect theelectrodes to the patient, as indicated in FIG. 3a. Diagram 37 (FIG. 1)on one of the electrodes is available to guide proper placement. Whenthe instrument detects that the electrodes have been connected, themessage indicated in FIG. 3b is displayed. This message directs theoperator to perform standard CPR operations on the patient. The operatorindicates that this step has been completed by pushing the YES switch.When the YES switch is pushed, or when 25 seconds has elapsed, themessage shown in FIG. 3c is displayed. If the subject is notunconscious, then the operator pushes the NO switch, and the messageshown in FIG. 3d will be displayed for a few seconds, after which themessage in FIG. 3c will reappear. This feature allows the operator torespond appropriately if the patient later loses consciousness.

If the patient is unconscious, or becomes unconscious, then the operatorpushes the YES switch (FIG. 3c), and the instrument enters a detectionmode in which the message shown in FIG. 3e is displayed. In this mode,electrocardiogram (ECG) and transthoracic impedance data is obtaineddirectly from the patient via electrodes 30 and 36 (FIG. 2). Theresulting data is used, together with information supplied by theoperator (e.g., subject unconscious), to determine whether adefibrillation shock is medically appropriate. During collection ofdata, the instrument looks for transthoracic impedance data that wouldindicate motion of the patient. If motion is detected, then the messageshown in FIG. 3f is displayed, and the data collection is restarted.

If the ECG data indicates that a defibrillation shock is notappropriate, then the message of FIG. 3d is briefly displayed, and thedefibrillator then returns to the state corresponding to FIG. 3b. If theinstrument determines that a shock is medically appropriate, then themessage of FIG. 3g is displayed, advising the operator to proceed bypushing the SHOCK switch. If the SHOCK switch is then pushed, theinstrument displays the message shown in FIG. 3h and then delivers adefibrillation shock to the patient. After the shock has been delivered,the instrument returns to the state corresponding to FIG. 3b. The cyclebeginning at FIG. 3b and ending at FIG. 3h may be repeated for a maximumof two additional times, if the patient remains unconscious.

CIRCUIT DESCRIPTION

The body 12 of the defibrillator houses the electronic componentsillustrated in FIGS. 4a and 4b. These components include data processor100, analog-to-digital converter (ADC) 102, processor controller 110,defibrillation circuit 120, analog preprocessor 140, data recorder 160,battery circuit 170, and various other components described below.Electrodes 30 and 36 are connected through electromagnetic interferencefilter 190 to defibrillation circuit 120 and to analog preprocessor 140.During the collection of ECG and transthoracic impedance data from thepatient, relay 122 is in the position shown in FIG. 4a. The analogpreprocessor separates the electrode signal into ECG and transthoracicimpedance components, and delivers the component signals to ADC 102 andto data recorder 160. When a shock is to be delivered, thedefibrillation circuit charges capacitor 126 up to a specified value,and then switches relay 122 such that capacitor 126 discharges throughthe patient via electrodes 30 and 36. After the shock has beendelivered, relay 122 returns to the position shown in FIG. 4a.

BATTERY CIRCUIT

The electronic circuit of the present invention is activated when coverplate 14 is removed from the unit. Removal of the cover plate causes thewithdrawal of pin 20, which in turn causes switches 176 and 178 (FIG.4b) to close, connecting recorder battery 172 to microcassette recorder161 and system battery 174 to the other components of the circuit inFIGS. 4a and 4b. The purpose of this feature is to prevent battery drainwhen the instrument is stored over extended periods of time. Means areprovided, however, for permitting a person to check the condition ofsystem battery 174 without opening or unsealing the instrument. Thismeans comprises magnetic reed switch 180 connected in parallel withswitch 178. The defibrillator of the present invention includes aseparate battery test card having small magnets imbedded therein. Totest the condition of system battery 174, a person holds the batterytest card at a designated position adjacent to the outer surface of body12. The magnet, indicated schematically by numeral 182 in FIG. 4b,closes reed switch 180 and provides power to all components of thedefibrillator with the exception of microcassette recorder 161. Theclosing of reed switch 180 also supplies a test signal to data processor100 on line 184. The test signal indicates to the data processor that atest is to be performed, and directs it to the appropriate procedure forcarrying out the test. If the test is successful, the data processorcauses tone generator 108 to emit a prescribed sequence of audibletones, to signal that the test has been successfully completed. Diode186 prevents a test signal from being applied to data processor 100during normal operation of the defibrillator, i.e., when switch 178 isclosed.

During operation of the defibrillator, battery level circuit 188continuously monitors the voltage available from system battery 174. Ifthe voltage of system battery 174 falls below the level required foroperation of data processor 100, then battery level circuit 188activates shutdown circuit 189. Shutdown circuit 189 responds by cuttingoff power to data processor 100, thus preventing operation of thedefibrillator at a voltage which might result in unreliable operation. Aback-up system for preventing defibrillator operation when the batterylevel is too low is provided by ADC 102. ADC 102 periodically samplesthe system battery voltage (B2) and provides the digitized samples todata processor 100 over bus 104. As described below, the data processorwill not advise or initiate a shock if such samples indicateinsufficient battery voltage.

ANALOG PREPROCESSOR

The function of the analog preprocessor is to supply a constant currentsignal to the electrodes and to analyze the return signal. If the returnsignal indicates that the electrodes are not connected to the patient,then the analog preprocessor sends a NOT CONNECTED signal to the dataprocessor. If the electrodes are connected, then the analog preprocessorextracts ECG signals and transthoracic impedance (TTI) signals from thereturn signal and sends the analog ECG and transthoracic impedancesignals to data recorder 160 and analog-to-digital converter (ADC) 102.

The analog preprocessor includes protection network 141, constantcurrent source 142, synchronous demodulator 144, amplifier/filters 146and 148, comparator 150, low pass filter 152, and amplifier/filter 154.Associated with the analog preprocessor is electromagnetic interferencefilter 190 consisting of inductor 192 and capacitor 194. Constantcurrent source 142 supplies a constant (RMS) current, 12 KHz sine wavewhich is applied to the patient through protection network 141 andelectrodes 30 and 36. The resulting signal is synchronously demodulatedby synchronous demodulator 144. The synchronous demodulator provides anoutput signal whose amplitude is proportional to the amplitude of the 12KHz component of the return signal, i.e., to the impedance betweenelectrodes 30 and 36. The output signal from synchronous demodulator 144is passed to amplifier/filter 146. Amplifier/filter 146 removes unwantedhigh frequency components, including any residual 12 KHz signal, andalso provides a small amount of gain. The output of amplifier/filter 146is fed to amplifier/filter 148 and to comparator 150. Amplifier/filter148 includes a bandpass filter with a passband of approximately 1-20 Hz.This filter thus removes the DC component from the return signal, andprovides an output indicative of transthoracic impedance variations overtime. Comparator 150 compares the level of the output ofamplifier/filter 146 with a fixed reference voltage. If the levelexceeds the reference, then the comparator pulls line 158 low, signalingthat the electrodes are not connected.

The signal from electrodes 30 and 36 is also input to low pass filter152 through protection network 141. The filter removes the 12 KHz signaland other high frequency components, and passes the resulting signal toamplifier/filter 154. Amplifier/filter 154 includes a bandpass filteradapted to extract the ECG signal returned from the patient through theelectrodes. As further described below, amplifier/filter 154 alsoprovides gain to the ECG signal, the amount of gain being determined bya digital GAIN SELECT signal originating in data processor 100 andtransmitted to amplifier/filter 154 over line 156.

Protection network 141 is a conventional impedance matching network thatprotects the analog preprocessor from the high voltage applied to theelectrodes by defibrillation circuit 120 during delivery of a shock tothe patient. Protection network 141 has an impedance that does notsignficantly affect ECG or transthoracic impedance measurements, butthat does cause the attenuation of the frequency components contained ina defibrillation pulse to a degree sufficient to prevent such a pulsefrom damaging any of the components of the analog preprocessor.

DATA PROCESSOR

Data processor 100 is a conventional digital computer that includes amicroprocessor, read only memory (ROM) for storing a program, randomaccess memory (RAM) for data storage, a parallel port and a timer. Asuitable microprocessor for use in data processor 100 is the NSC 800microprocessor available from the National Semiconductor Corporation.

Associated with data processor 100 are processor controller 110 andassociated SHOCK pushbutton switch 56, display system 106, tonegenerator 108, YES and NO pushbutton switches 52 and 54, and ADC 102.Processor controller 110 coordinates the activities of data processor100 and defibrillation circuit 120, and is described in greater detailbelow. Display system 106 comprises a conventional display driver andLCD display unit 50 (FIG. 2). Tone generator 108 is a conventional audiotransducer used for producing audible signals. Pushbutton switches 52,54 and 56 correspond to the pushbuttons shown in FIGS. 2 and 3, and areused by the operator to respond to prompts communicated through displaysystem 106, and to initiate a defibrillation shock. ADC 102 is ananalog-to-digital converter used for converting the analog TTI and ECGsignals from analog preprocessor 140 into digital signals usable by dataprocessor 100. ADC 102 alternately samples the TTI and ECG signals at240 Hz, thus providing a sampling rate of 120 Hz for each signal. Thedigital samples are passed to the data processor over 8-bit bus 104. ADC102 provides an interrupt signal RSTC to data processor 100 each time adigital sample is ready. In response to the RSTC interrupt, dataprocessor 100 jumps to an interrupt service routine for inputting thesample. Through this arrangement, a uniform sampling rate is providedregardless of the timing of the program for operating data processor100.

DEFIBRILLATION CIRCUIT

Defibrillation circuit 120 is activated by a high ENABLE signal on line134. In response to such a signal, the defibrillation circuit beginscharging capacitor 126 from system battery 174 (B2). When the chargereaches a predetermined threshold, the defibrillation circuit energizesrelay 122, discharging capacitor 126 through the patient throughelectrodes 30 and 36.

The defibrillation circuit is activated by a high ENABLE signalmomentarily appearing on line 134. In response to this signal, bistablecontrol circuit 124 latches line 134 into a high state, and causescharge transfer circuit 128 to begin charging capacitor 126 from systembattery supply B2. Bistable control circuit 124 may, by way of example,consist of two amplifiers connected in series, with positive feedbackmeans provided to enable the circuit to be stable in either one of twostates. Charge transfer circuit 128 may be any well known circuit forconverting a low level DC voltage to a high voltage output by means of aflyback transformer or other conventional means.

As capacitor 126 is charged through charge transfer circuit 128, thevoltage on capacitor 126 is continuously monitored by comparator/timer130. When the capacitor voltage exceeds a threshold level,comparator/timer 130 triggers relay driver 132 which in turn energizesthe coil of relay 122, switching the relay and connecting capacitor 126to the electrodes. The capacitor then discharges through the patient viawave shaping inductor 138. At the same time that comparator/timer 130triggers relay driver 132, it also pulls line 134 low Bistable controlcircuit 124 then latches line 134 into a low state, completing thedefibrillation cycle. Should capacitor 126 fail to charge to thethreshold level within a predetermined time interval, then a timeoutcircuit included within comparator/timer 130 triggers relay driver 132and pulls line 134 low, thus delivering to the patient whatever energyis available and terminating the defibrillation cycle.

As previously described, analog preprocessor 140 pulls line 158 low whenit detects that electrodes 30 and 36 are not connected to the patient.One effect of line 158 going low is that line 134 is also pulled lowthrough diode 136. A low voltage on line 134 will cause bistable controlcircuit 124 to latch line 134 in its low state, terminating anydefibrillation cycle that is in process. Thus the defibrillator of thepresent invention will not attempt to deliver a defibrillation pulseshould the electrodes become disconnected. Line 134 is also connected tobattery level circuit 188 through diode 137. Thus when battery levelcircuit 188 detects a low voltage on system battery B2, line 134 will beheld low, and the delivery of a defibrillation shock will also beprevented in this circumstance.

PROCESSOR CONTROLLER

Processor controller 110 coordinates the activities of data processor100 and defibrillation circuit 120. When the data processor determinesthat a shock is advised (see FIG. 3g), it sends a high SHOCK ENABLEsignal to processor controller 110 on line 200. This signal activatesSHOCK pushbutton switch 56, such that if switch 56 is now pushed, a highENABLE signal will be sent to defibrillation circuit 120 on line 134,initiating a defibrillation cycle. At the same time that line 134 isdriven high, processor controller 110 sends a low READY signal back todata processor 100 on line 202. A short time after the READY signal issent, processor controller sends a low SHUT DOWN signal on line 204. TheSHUT DOWN signal causes data processor 100 to go into a quiescent statein which only its timer continues to be active. The READY signal is usedby data processor 100 to prepare for entering this quiescent state. Thepurpose of this feature is to prevent any electromagnetic interferencethat might accompany the delivery of a shock to interfere with theoperations of the data processor. After a shock has been delivered,processor controller 110 pulls lines 202 and 204 high to restart thedata processor, and then issues a high RSTA interrupt signal on line206, causing the data processor to go back to the state corresponding tothe display in FIG. 3b, starting another cycle.

The detailed construction of processor controller 110 is illustrated inFIG. 5. A high SHOCK ENABLE signal appearing on line 200 causes inverter210 to supply a low voltage to terminal 214 of shock switch 56. Whenshock switch 56 is closed, terminal 216 is also driven low, enablingcapacitor 218 to rapidly charge through switch 56. The resulting lowvoltage is input to inverter 222 through input resistor 220, drivingline 134 high through resistor 224 and diode 226. When switch 56 isreleased, capacitor 218 discharges through resistor 228 at a rate slowenough to enable bistable control circuit 124 (FIG. 4a) to latch line134 into a high state. After capacitor 218 discharges, diode 226provides isolation between line 134 and inverter 222. Diode 212 preventscapacitor 218 from discharging through switch 56.

The high voltage on line 134 is sensed by inverter 232 through inputresistance 234, causing inverter 232 to drive line 202 low. A low signalon line 202 causes data processor 100 to execute various housekeepingsteps in preparation for line 204 going low. A low signal on line 202also causes capacitor 236 to begin charging through resistor 238 andthrough resistor 240 and diode 242. The decreasing voltage at node 243is coupled to inverter 244 through input resistor 246. When the voltageat node 243 has dropped below a certain level, a low signal appears online 204, halting the operations of data processor 100. The delaybetween the SHUT DOWN and READY signals is determined by the timeconstant for the charge of capacitor 236.

At the time that line 204 is pulled low, node 250 goes high, andcapacitor 252 begins to charge through resistor 254. The rising voltageat node 260 is coupled to inverter 256 through input resistor 258. Whenthe voltage of node 260 has risen to a sufficient level, inverter 256causes a low RSTA signal to appear on line 206. Since data processor 100is shut down, the low RSTA signal has no effect at this time.

When a defibrillation cycle is completed, or when a low battery or a NOTCONNECTED signal is provided by analog preprocessor 140, line 134 ispulled low. Such a low signal initiates a sequence of events which isthe reverse of that just described. In particular, a low signal on line134 immediately drives line 202 high, and drives line 204 high a shorttime later, restarting the data processor. After another short timeinterval, processor controller 110 sends a high RSTA interrupt signal online 206, vectoring data processor 100 to an appropriate restart pointas described below.

DATA RECORDER

Data recorder 160 comprises microcassette recorder 161,multiplexer/modulator 162, audio amplifier 163, microphone 164, andcoupling capacitor 165. Microcassette recorder 161 is powered byseparate recorder battery (B1) 172, which is connected to themicrocassette recorder through a normal conductor line 166 and throughfusible link 167. Fusible link 167 consists of a piece of thin wire thatmelts as soon as current begins to flow through it, i.e., when coverplate 14 is removed and switch 176 closes. Prior to melting, fusiblelink 167 holds spring loaded pinch roller 168 out of engagement with thetape and capstan of microcassette recorder 161. This feature is providedso that the defibrillator of the present invention will be usable afteran extended period of storage. During use, pinch roller 168 provides thepressure between the tape and capstan to enable the capstan to drive thetape. Prior to use, however, the fusible link holds the pinch rollerdisengaged from the capstan and tape to prevent it from flattening andsticking to the tape.

Microcassette recorder 161 is a two track recorder, one track fortransthoracic impedance and ECG data, and the second track for voice andstatus information. Multiplexer/modulator 162 receives the analogtransthoracic impedance and ECG signals from analog preprocessor 140,converts these analog signals to pulse-width modulation format, andmultiplexes the resulting pulse streams for recording on one track ofmicrocassette recorder 161. The other track of the microcassetterecorder records voice and other audio signals picked up by microphone164 and amplifier by audio amplifier 163. The voice track also recordssystem status information sent by data processor 100 through line 169.The status information is coupled from line 169 to audio amplifier 163through coupling capacitor 165.

The defibrillator of the present invention includes means by which datarecorder 160 can record information confirming that a substantial amountof energy, i.e., a defibrillation pulse, has actually been delivered tothe patient through electrodes 30 and 36. Referring to FIG. 6, a crosssection of wave shaping inductor 138 is shown including bobbin 272 andinductor coils 270. The central portion of bobbin 272 is indented toform recess 274. Elastic cord 276 is mounted to bobbin 272 over recess274, and mounts ferrous objects 278 thereon such that the ferrousobjects are normally held over the recess spaced apart from the bobbin.

When a defibrillation pulse is delivered through wave shaping inductor138, the current through inductor coils 270 creates a maximum magneticfield density in the direction indicated by arrow 280 that pulls ferrousobjects 278 with considerable force into bobbin 272 at the base ofrecess 274. The unique sound caused by the objects striking the bobbinis picked up by microphone 164 and recorded on the voice track ofmicrocassette recorder 161. These sounds can later be identified toconfirm that defibrillation pulses have actually been delivered. After adefibrillation pulse, ferrous objects 278 return to the positionindicated in FIG. 6, ready for a subsequent pulse to be recorded.

DATA PROCESSOR OPERATION

FIGS. 7a through 7f illustrate a flow chart for a program suitable foroperation of the microprocessor of data processor 100. Block 300represents the point at which program execution begins when power isfirst supplied to the microprocessor, or when line 204 (FIG. 4b) goeshigh. Block 302 tests the status of line 184 (FIG. 4b) to determinewhether the power-on is a result of a test or actual operation of thedevice. If it is a test, then control passes to block 304 whereappropriate tests are performed to verify that system battery 174 hassufficient voltage and that data processor 100 is capable of properoperation. In one embodiment, block 304 tests a digitized batteryvoltage sample provided by ADC 102 over bus 104. Block 306 determineswhether the tests have been successfully passed. If they have not, thencontrol returns to block 304 and the tests are repeated. If the testsare passed, then block 308 causes tone generator 108 to beep threetimes, block 310 delays program execution for three seconds, and controlthen returns to block 304 to repeat the tests. In the usual case, theperson performing the test procedure will remove the magnet (test card)182 when the beeps are generated, terminating the test and shutting downthe system. If the three beeps are not heard, it is an indication thatthe tests have not been passed and that maintenance is required.

When the power-on (in block 300) is due to an actual opening of thedefibrillator, then control passes from block 302 to block 312 wherevariable CPR is set to 1. This variable controls the number of timesthat the CPR sequence (FIG. 3b) is repeated, as described below. Block316 then enables interrupts RSTA and RSTB. Interrupt RSTA is used torestart the microprocessor after a defibrillation shock has beendelivered. The RSTA restart point is indicated by entry point 314, sothat program execution returns at block 316 after a shock has beendelivered. Referring to FIGS. 4a and 4b, interrupt RSTB is providedwhenever a NOT CONNECTED signal is generated by analog preprocessor 140.In response to an RSTB interrupt, the microprocessor executes theinterrupt service routine shown in FIG. 7f, and then returns control tothe main program at entry point A, recommencing execution with block312.

When the defibrillator is first opened for actual operation, electrodes30 and 36 will not be connected, and the analog preprocessor will pullline 158 low, causing an RSTB interrupt signal to be sent to dataprocessor 100. In this circumstance, the enabling of interrupt RSTB inblock 316 will cause an immediate jump to block 452 of the interruptservice routine of FIG. 7f. Block 452 generates the display shown inFIG. 3a, and block 454 checks to see whether 20 seconds have elapsedsince the defibrillator was opened. If 20 seconds have not elapsed,program execution is delayed for one second by block 456, after whichprogram flow returns to block 312 in FIG. 7a. If the electrodes are notyet connected, interrupt RSTB will immediately vector the program backto the interrupt service routine, and this loop will continue until theelectrodes are connected and interrupt RSTB is no longer present. Forthe first 20 seconds after the device is opened, block 454 causes a jumpdirectly to block 456 each time the interrupt service routine isexecuted. Between 20-25 seconds after the device is opened, blocks 454and 458 direct control through block 460 and a series of beeps isproduced. After 25 seconds the beeps terminate and the program loopsbetween the interrupt service routine and the main routine until theelectrodes are connected.

When the electrodes are connected, interrupt RSTB is no longer presentand control passes through block 316 to block 318, where the messageindicated in FIG. 3b is displayed. Block 320 then causes generation of acharacteristic tone sequence, and block 322 tests to see whether YESpushbutton switch 52 has been pressed. When the YES switch is pushed, orwhen 25 seconds have elapsed, control passes to block 324 where thenumber of passes through the loop consisting of blocks 316-322 iscompared to variable CPR. After a poweron, this test will be satisfiedafter the first pass, since CPR was set to 1 in block 312. Whenever thistest is not satisfied, program execution returns to block 316, andanother CPR sequence is performed. When the number of CPR sequencesspecified by variable CPR have been completed, control passes to block326 which checks the number of shocks that have been delivered. Thedefibrillator of the present invention is intended to deliver up to amaximum of three defibrillation shocks. If three shocks have alreadybeen delivered, then block 326 returns control to block 316, and the CPRsequence is continued indefinately. If three shocks have not beendelivered, then control passes to block 328, where the voltage level ofsystem battery 174 is checked by examining the battery voltage sampleprovided by ADC 102 over bus 104. If the battery level is too low forreliable operation, then the CPR sequence continues as indicated. If thebattery level is sufficient, then control passes to block 330 (FIG. 7b).

Block 330 prompts the operator to indicate whether or not the patient isunconscious. After generating this display, block 332 directs programexecution to either block 338 or 334, depending upon whether or not theoperator indicated that the patient was conscious the last time thequestion in block 330 was answered. If the patient was not conscious inthe previous pass, then block 334 outputs a characteristic tonesequence. As indicated by block 336, this tone sequence continues untilthe operator responds by pushing either the YES or NO pushbutton switch.When the operator does respond, control passes to block 340. When thepatient was conscious in the previous pass, then control passes directlyfrom block 332 to block 338, where the program loops until the operatorresponds and then continues to block 340.

Block 340 determines whether the operator of the defibrillator hasindicated that the patient is unconscious. If the patient is notunconscious, then block 342 outputs the display indicated in FIG. 3d,block 344 outputs a characteristic tone sequence, block 346 causes afour second delay, and program execution returns to block 330 to againask whether the patient is unconscious. By such means, the defibrillatorwill be prepared to respond in an appropriate manner should a presentlyconscious patient later lose consciousness.

If the patient is unconscious, control passes to block 350 (FIG. 7c),and the message indicated in FIG. 3e is displayed. Block 352 thenoutputs a single tone through tone generator 108, and the programcommences the collection of TTI (transthoracic impedance) and ECG datafrom the unconscious patient. As described previously, ADC 102alternately supplies digital TTI and ECG samples to data processor 100,issuing interrupt signal RSTC whenever a sample is ready. Block 354enables the RSTC interrupt, and the program then waits in block 356 forTTI data to be supplied. When an RSTC interrupt is received, programcontrol is vectored to RSTC entry point 358, the data sample is input byblock 360, and block 362 determines whether the sample is TTI or ECGdata. If the sample is TTI data, then execution continues with block364.

Block 364 analyzes successive TTI values to determine whether excessivemotion is present in the patient. By way of example, block 364 coulddetect excessive motion by determining whether the last two TTI valuesexceed a threshold. If excessive motion is present, then block 366generates the display indicated in FIG. 3f, block 368 causes productionof a steady tone by tone generator 108, block 370 causes a one seconddelay, and block 372 determines whether the excessive motion has beenpresent for 15 seconds. If it has not been present for 15 seconds, theprogram returns to block 350, and the data collection sequence is begunagain. If excessive motion has been present for 15 or more seconds, thenthe program returns to block 316 (FIG. 7a), corresponding to the displayin FIG. 3b.

The defibrillator of the present invention checks the patient forexcessive motion because such motion could result in invalid ECG data,and because excessive motion could indicate that the patient should notbe shocked. For example, excessive motion could indicate that thepatient is conscious, that the patient is being moved, or that thepatient is moving internally due, for example, to cardiac output.

If excessive motion is not present, then the defibrillator waits inblock 374 for ECG data. When such data is ready, it is input by block360, and block 362 directs program flow to block 376. Block 376attenuates 60 Hz noise in the ECG data, and block 378 then tests theamplitude of the most recent ECG data point. If the amplitude is toolarge, block 380 decreases the gain of the analog preprocessor 140 bymodifying gain select signal 156 (FIGS. 4a and 4b), and data collectionis restarted at block 350. If the ECG amplitude is not too large, thenblock 382 provides a second level of filtering adapted to remove rumblebelow the ECG frequency range. If there is more data to be collected,block 384 then returns control to block 356 for acquisition of the nextTTI and ECG data samples. When a sufficient number of ECG data sampleshave been collected and stored, control passes to block 386 in FIG. 7d.

Block 386 disables interrupt RSTC, thereby preventing ADC 102 fromsubsequently interrupting program flow. Block 388 then analyzes the ECGdata points to determine the repetition rate (frequency) of the dominantcomplex in the ECG signal (e.g., the QRS complex). If the rate is lessthan 2.3 Hz or greater than 12 Hz, then block 390 directs program flowto block 392, where the shock flag for this pass is set to zero,indicating that the patient is not presently in a shockable condition.If the rate is within the shockable range, then block 394 checks to seewhether the frequency variance of the ECG data exceeds a maximum limit.If the variance is too large, then the shock flag is set to zero inblock 392. If the frequency variance is consistent with the applicationof defibrillation shock, then block 396 checks the average amplitude ofthe ECG signal. If the average amplitude is too low, then no conclusionscan be reliably drawn from the data, and the shock flag is set to zero.If the amplitude is sufficient, block 398 determines whether R waves arepresent in the ECG signal. If R waves are present, then the patientshould not be shocked, and the shock flag is set to zero in block 392.If R waves are not present, then block 400 performs a slope histogramanalysis of the ECG data. In this analysis, the differences betweenadjacent ECG data points are determined, and the slopes (differences)falling within a series of ranges are counted. Block 402 then checks therelative frequency of low slope values. If such relative frequency istoo high to be consistent with a shockable arrhythmia, then the shockflag is set to zero in block 392. If the relative frequencies of thelower histogram ranges are within shockable limits, then block 404 setsthe shock flag for this pass to one, signifying that the patient's ECGsignal indicates that a defibrillation shock is medically appropriate.It is to be understood that other known tests could be used, eithersingly or in combination, to determine whether a shockable ECG rhythm ispresent, and the invention herein is not limited to any particularmethod of making this determination.

The defibrillator makes two or three successive passes through the dataacquisition and analysis steps just described. When the first pass iscomplete, blocks 406 and 408 direct program flow to block 350 (FIG. 7c)to begin the second pass. When the second pass is complete, block 410checks the shock flag for the second pass. If the second shock flag isnot equal to one, then control passes to block 438 (FIG. 7e) and a SHOCKNOT REQUIRED message is displayed to the operator. If both the first andsecond shock flags are equal to one, then control passes to block 416(FIG. 7e), and a shock sequence is commenced. If the second shock flagis one, but the first shock flag is zero, then control returns to block350, and a third pass is commenced. When the third pass is complete,block 406 directs control to block 414, and the third shock flag istested to determine whether or not a shock should be administered.

If a shock is to be administered, then block 416 causes the dataprocessor to drive line 200 high (FIG. 4b), enabling SHOCK pushbuttonswitch 56. Block 418 then causes generation of the display indicated inFIG. 3g, and block 420 causes production of a characteristic tonesequence. The program then executes a loop consisting of blocks 422 and424 until the operator pushes the shock switch, or until 30 seconds haveelapsed. If the shock switch is pushed, block 426 causes generation ofthe display indicated in FIG. 3h, block 428 causes output of a warningtone, block 430 sets variable CPR to 2, and block 432 then waits forprocessor controller 110 to issue READY and SHUT DOWN signals, aspreviously described. If the operator does not push the SHOCK switchwithin 30 seconds, block 434 causes line 200 to be pulled low, disablingthe SHOCK switch. Block 436 then sets variable CPR equal to 4, andreturns control to the CPR sequence commencing with block 316 (FIG. 7a).

If the tests shown in FIG. 7d indicate that a shock is not to beapplied, then control passes to block 438 where the indicated message isdisplayed. Block 440 then causes output of a characteristic tonesequence, and block 442 causes a 5 second delay. Block 436 then setsvariable CPR to 4, and control returns to block 316. The values of CPRset in blocks 430 or 436 will subsequently result in block 324 causingeither 2 or 4 CPR sequences to be executed, depending upon whether ornot a shock was administered to the patient.

While the preferred embodiments of the invention have been illustratedand described, it should be understood that variations will becomeapparent to those skilled in the art. Accordingly, the invention is notto be limited to the specific embodiments illustrated and describedherein, but rather the true scope and spirit of the invention are to bedetermined by reference to the appended claims.

The embodiments of the invention in which an exclusive property orpriviledge is claimed are defined as follows:
 1. An interactive medicalelectronic device for obtaining information about a patient's conditiondirectly from the patient and information pertinent to an analysis ofthe patient's condition indirectly through an operator of the device,and for producing a medically appropriate action in response thereto,said device comprising:(a) sensor means for obtaining direct informationconcerning the condition of the patient; (b) information processingmeans, comprising:(i) interactive communication means including meansfor obtaining indirect information pertinent to an analysis of thepatient's condition from the operator, the means for obtaining indirectinformation comprising means for prompting the operator, and means forreceiving the operator's response thereto; and (ii) control means forproducing a control signal when said direct and indirect informationindicates that the medically appropriate action should be taken; and (c)output means responsive to the control signal for producing said actionupon the patient.
 2. The device of claim 1, wherein the means forprompting the operator comprises means for communicating questions tothe operator.
 3. The device of claim 2, wherein the means for obtainingindirect information comprises means for communicating questions forwhich appropriate responses are either YES or NO.
 4. The device of claim3, wherein the means for receiving the operator's responses comprisesfirst and second touch activated means, the first touch activated meanscorresponding to a YES response and the second touch activated meanscorresponding to a NO response.
 5. The device of claim 1, wherein theinteractive communication means includes means for communicatinginstructions to the operator.
 6. The device of claim 1, wherein theinformation processing means comprises means for obtaining the assent ofthe operator before producing the control signal.
 7. The device of claim1, wherein the sensor means comprises means for detecting the electricalactivity of the patient's heart.
 8. The device of claim 7, wherein theoutput means comprises means for applying a defibrillation pulse to thepatient.
 9. The device of claim 8, wherein the means for determiningindirect information comprises means for obtaining informationindicating whether or not the patient is conscious.
 10. The device ofclaim 9, wherein the means for obtaining indirect information comprisesmeans for obtaining information indicating whether or notcardiopulmonary resuscitation has been performed on the patient.
 11. Thedevice of claim 8 or 10, wherein the interactive communication meansincludes means for communicating instructions to the operator.
 12. Thedevice of claim 11, wherein the interactive communication means includesmeans for instructing the operator to perform cardiopulmonaryresuscitation on the patient.
 13. The device of claim 8, wherein theinformation processing means comprises means for communicating aquestion regarding whether or not the patient is conscious, and meansresponsive to a response indicating that the patient is conscious forpreventing production of the control signal and for continuing tocommunicate the said question regarding whether or not the patient isconscious, such that if the patient subsequently becomes unconscious theoperator can respond appropriately.
 14. The device of claim 8, whereinthe information processing means comprises means for obtaining theassent of the operator before producing the control signal.
 15. Thedefibrillator of claim 8, wherein the means for applying adefibrillation pulse includes energy storage means and means responsiveto the control signal for charging the energy storage means up to athreshold level and then discharging the energy storage means throughthe patient without operator intervention.
 16. The device of claim 1,wherein the sensor means comprises electrodes adapted to receiveelectric signals including an electrocardiogram signal from the patient,and electrocardiogram detection means connectable to the electrodes forreceiving electrical signals from the electrodes and producing an ECGsignal corresponding to the patient's electrocardiogram signal.
 17. Thedevice of claim 16, wherein the output means comprises means connectableto the electrodes for applying a defibrillation pulse to the patientthrough the electrodes.
 18. The device of claim 17, wherein the sensormeans comprises motion detection means connectable to the electrodes forproducing a motion signal indicative of patient motion including patientmotion not synchronized with the ECG signal, and wherein the controlmeans comprises means for preventing the production of the controlsignal when excessive patient motion is detected.
 19. The device ofclaim 18, wherein the control means comprises means for analyzing theECG signal to detect the presence or absence of a shockable heartrhythm, means for analyzing the motion signal to detect the presence orabsence of excessive motion, and means for producing the control signalonly if shockable heart rhythm is present and if excessive motion isabsent.
 20. The device of claim 19, wherein the means for analyzing theECG signal is adapted to analyzing the ECG signal during a predeterminedlength of time, and wherein the means for analyzing the motion signalincludes means for terminating the analysis of the ECG signal when thepresence of excessive motion is detected, whereby the control signal isnot produced if excessive motion is detected.
 21. A defibrillator fordelivering a defibrillation shock to a patient, comprising:informationprocessing means for determining whether a defibrillation shock shouldbe delivered and for providing a first control signal if saiddefibrillation shock should be delivered; and defibrillation meansincluding energy storage means and charge control means responsive tothe first control signal for charging the energy storage means and thendischarging the energy storage means through the patient, the chargecontrol means being operative to discharge the energy storage meansthrough the patient when the charge on the energy storage means reachesa threshold level or when a predetermined time has elapsed after thefirst control signal, whichever occurs first.
 22. The defibrillator ofclaim 21, wherein the defibrillation means comprises means for providinga second control signal whenever the energy storage means is discharged,and wherein the information processing means includes means forsuspending its operations from the time that the first control signal isprovided until the second control signal is provided.
 23. Thedefibrillator of claim 22, wherein the first and second control signalsare communicated between the information processing means and thedefibrillation means through a single conductive line.